The chemical basis for interaction between steroid hormones and specific serum proteins is being investigated. Progesterone-binding globulin and alpha-1-glycoprotein have been isolated as homogeneous proteins. They are being studied by physicochemical and chemical methods for relationship of chemical structure to steroid binding. BIBLIOGRAPHIC REFERENCES: Kute, T. and U. Westphal. Steroid-Protein Interactions. XXXIV. Chemical Modification of alpha-1-Acid Glycoprotein for Characterization of the Progesterone Binding Site. Biochim. Biophys. Acta 420, 195-213 (1976). Cheng, S. L., S. D. Stroupe and U. Westphal. Steroid-Protein Interaction (XXXV). Purification of Progesterone-Binding Globulin by Affinity Chromatography. FEBS Letters 64, 380-384 (1976).